1. Field of the Invention
The present invention generally relates to image capture systems and methods and, more particularly, to capturing a full color or monochrome image of a target and/or capturing a monochrome image of an optical code symbol to be read using a common imaging array, and especially by using an imaging array of pixel sensors each operative for measuring each of three primary colors of incident light at the same location of a respective pixel sensor.
2. Description of the Related Art
Optical codes are patterns made up of image areas having different light-reflective or light-emissive properties, which are typically assembled in accordance with a priori rules. The term “barcode” is sometimes used to describe certain kinds of optical codes. The optical properties and patterns of optical codes are selected to distinguish them in appearance from the background environments in which they are used. Systems for identifying or extracting data from optical codes are sometimes referred to as “optical code readers” of which barcode scanners are one type. Optical code readers are used in both fixed or portable installations in many diverse environments such as in stores for check-out services, in manufacturing locations for work flow and inventory control, and in transport vehicles for tracking package handling. The optical code can be used as a rapid, generalized means of data entry, for example, by reading a target barcode from a printed listing of many barcodes. In some uses, the optical code reader is connected to a portable data processing device or a data collection and transmission device. Frequently, the optical code reader includes a hand-held sensor which is manually directed at a target code.
Most conventional optical scanning systems are designed to read one-dimensional barcode symbols. The barcode is a pattern of variable-width rectangular bars separated by fixed or variable width spaces. The bars and spaces have different light-reflecting characteristics. One example of a one-dimensional barcode is the UPC/EAN code used to identify, for example, product inventory. An example of a two-dimensional or stacked barcode is the PDF417 barcode. A description of PDF 417 barcode and techniques for decoding it are disclosed in U.S. Pat. No. 5,635,697. Another conventional optical code is known as “MaxiCode”. It consists of a central finder pattern or bull's eye center and a grid of hexagons surrounding the central finder. It should be noted that the aspects of the inventions disclosed in this patent application are applicable to optical code readers, in general, without regard to the particular type of optical codes which they are adapted to read. The invention described is also applicable to some associated image recognition or analysis.
Most conventional scanning systems generate one or more beams of laser light which reflects off a barcode symbol and back to the system. The system obtains a continuous analog waveform corresponding to the light reflected by the code along one or more scan lines of the system. The system then decodes the waveform to extract information from the barcode. A system of this general type is disclosed, for example, in U.S. Pat. No. 4,251,798. A beam scanning system for detecting and decoding one-and two-dimensional barcodes is disclosed in U.S. Pat. No. 5,561,283.
Many scanning systems in use today employ a scanning laser beam. Some such systems are deployed in hand-held units which may be manually pointed at a target. Often an individual system is a component of a much larger network including other scanners, computers, cabling, data terminals, etc.
Barcodes can also be read by employing imaging devices. For example, an image sensor device may be employed which has a two-dimensional array of cells or photosensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor device may include a two-dimensional or area charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) device and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view.
It is therefore known to use a CCD for capturing a monochrome image of a barcode symbol to be read as, for example, disclosed in U.S. Pat. No. 5,703,349. It is also known to use a CCD with multiple buried channels for capturing a full color image of a target as, for example, disclosed in U.S. Pat. No. 4,613,895.
Due to the difficulties and expense of making such CCDs, it is known from U.S. Pat. No. 3,971,065 to use a color filter mosaic to select different wavelength bands at different cell locations. One popular mosaic used in digital cameras is the Bayer color filter array (CFA) pattern having 50% green pixels arranged in a checkerboard and alternating lines of 25% red and 25% blue pixels filling the remainder of the pattern.
Although generally satisfactory for its intended purpose, the Bayer CFA has color aliasing, resolution and sensitivity problems due in part to the fact that the cells for the different colors are at different locations. To alleviate such problems, the prior art has proposed in U.S. Pat. No. 5,965,875 an imaging array of pixel sensors, each having three photosensors for measuring the different colors at the same location, that is, at each pixel sensor, by using a triple-well, integrated circuit structure.
Thus, it is known to use a two-dimensional imaging sensor device in a barcode symbol reader or in a digital camera. Digital photographs are better taken with an image capture system focused far from the camera at infinity with a relatively large aperture for collecting light. Barcode symbols are better read with an image capture system focused close to the reader with a relatively smaller aperture due to a depth of field requirement to keep a working distance range of the reader within practical limits. By way of example, the working distance of a reader typically lies in the range from about 0.5″ to about 12″, whereas the working distance range of a camera typically lies in the range from about 12″ to infinity.
These conflicting requirements have led to arrangements that utilize moving optical elements to change the focus of the image capture system when a barcode reader and a camera are built into a single, portable device. It is known to use sound- or light-based, auto-focusing mechanisms in a camera to detect the distance to a target and vary the focus accordingly. It is also known to slide or move lenses or glass plates in a barcode reader to vary the focus. However, all of these designs require moving parts which are complex to assemble, and often exhibit poor reliability and repeatability.